It's in a facility called Building 18, which cost taxpayers $214 million.

And now, the Biosafety Level 3 lab at the Centers for Disease Control and Prevention in Atlanta is also the subject of a congressional investigation after a potentially dangerous airflow leak at that lab, CNN has learned.

The leak occurred on February 16, when air flowed the wrong way out of a germ lab into a clean-air corridor, rather than through the powerful HEPA filter that cleans the air, congressional sources and CDC officials said. Visitors touring the facility were in the clean corridor when they observed a puff of air being pushed out from the lab through a slot in a door window.

If experiments had been under way at the time of that air leak, experts say, unprotected visitors could have been exposed to deadly germs, although an epidemic would have been unlikely.

According to U.S. Rep. Michael Burgess, a Texas Republican and a medical doctor, the House Energy and Commerce Committee has asked the CDC for documents about that incident. The request came in the wake of a report on internal CDC e-mails about the incident, first reported by USA Today last week.

"The biggest concern was that there was a contingent of visitors who were walking through the building," Burgess said. "And had one of those people been stricken or made ill or worse, obviously that would have been devastating."

The lab handles small mammals such as rats, ferrets and mice as part of its experiments with pathogens, according to CDC officials. They say animals were in the lab at the time of the air leak, but they were secured in filtered cages.

CDC officials say the lab was clean, was not active at the time, and no one got infected.

"At no time during recent incidents featured in the media were CDC workers or the public in harm's way," agency spokesman Tom Skinner said. "This unique facility features multiple security layers specifically designed to protect workers and the public in the event of an incident."

In a statement released to CNN, Burgess' committee said, "We will actively work to find out if there are additional concerns or incidents associated with Building 18. Any anomaly or breach is of concern, and we will work to ensure the integrity of the facility is maintained and that our scientists are safe."

There has been at least one other safety-related incident in that same building where February's air leak occurred.

In 2008, it was discovered that a high-containment lab door was sealed with duct tape. That incident was first reported by the Atlanta Journal-Constitution and confirmed to CNN by Skinner.

Robert Hawley, former safety chief at the U.S. Army Medical Research Institute of Infectious Diseases, said the CDC has many safety layers in place at its labs. Hawley says researchers at the Biosafety Level 3 lab work in biosafety "cabinets" within the lab itself.

"Nothing is handled outside that cabinet," Hawley said. "So they're working with minute amounts of material, and the chances of aerosol are negligible."

But there are questions about a possible cover-up.

In an internal e-mail, reported by USA Today, CDC biologist Kismet Scarborough said the centers "... will do anything ... to hide the fact that we have serious problems with the airflow and containment in this whole building."

CNN has not been able to independently verify that e-mail. But in response, Skinner said, "CDC will continue to take an open, transparent and inclusive approach to address any safety challenge in a manner that will ensure the safety of our workforce and the public."

Skinner said the agency "intends to cooperate fully with Rep. Burgess and the committee to address any questions they may have about Building 18 at CDC."